Vulcan desert soft-suit

Young Spock and adult Spock wearing desert soft-suits

A Vulcan desert soft-suit was a type of clothing worn by Vulcans to enable them to survive the harsh desert conditions of Vulcan's Forge.

Spock, as an adult, and his younger self wore desert soft-suits while they were in The Forge. The older Spock's suit had been provided by the USS Enterprise's wardrobe section. (TAS: "Yesteryear")